1. Field of the Invention
The present invention relates to a magneto-resistive effect element and a magnetic memory.
2. Related Art
A magneto-resistive effect element having magnetic films is used for a magnetic head, a magnetic sensor and so forth, and it has been proposed to be used for a solid magnetic memory (magneto-resistive effect memory: MRAM (Magnetic Random Access Memory)).
In recent years, a ferromagnetic tunnel junction element or the so-called “tunneling magneto-resistive element (TMR element)” has been proposed as a magneto-resistive effect element utilizing a tunnel current and having a sandwiching structure where one dielectric is inserted between two ferromagnetic metal layers, and a current is caused to flow perpendicular to a film face to utilize a tunneling current. In the tunneling magneto-resistive element, since a magneto-resistance change ratio (MR ratio) has reached 20% or more, a possibility of the MRAM to public application is increasing.
The TMR element is realized by the following method. That is, after a thin AL (aluminum) layer having a thickness of 0.6 nm to 2.0 nm is formed on a ferromagnetic electrode, and the surface of the Al layer is exposed to oxygen glow discharge or an oxygen gas to form a tunnel barrier layer consisting of Al2O3.
Further, a ferromagnetic single tunnel junction having a structure where a magnetization direction of one of ferromagnetic layers constituting the ferromagnetic single tunnel junction is pinned by an anti-ferromagnetic layer has been proposed.
Further a ferromagnetic tunnel junction obtained through magnetic particles diffused in a dielectric material and a ferromagnetic dual tunnel junction have been also proposed.
In view of the fact that a magneto-resistance change ratio in a range of 20% to 50% have been also achieved in these tunneling magneto-resistive elements and the fact that reduction in magneto-resistance change ratio can be suppressed even if a voltage value to be applied to a tunneling magneto-resistive element is increased in order to obtain a desired output voltage value, there is a possibility of the TMR element to application to the MRAM.
A magnetic recording element using the ferromagnetic single tunnel junction or the ferromagnetic dual tunnel junction is nonvolatile and has a short write/read time of 10 ns or less and potential, i.e., can be rewritten 1015 or more. In particular, in a magnetic recording element using a ferromagnetic dual tunnel junction, as described above, a decrease in magneto-resistance change ratio can be suppressed even though a voltage applied to the ferromagnetic tunnel junction element is increased to obtain a desired large output voltage, and preferable characteristic for a magnetic recording element can be achieved.
However, regarding a cell size of the memory, when an architecture where a cell is constituted by one transistor and one TMR element is used, it is disadvantageously impossible to make a memory cell size smaller than the size of a semiconductor DRAM (Dynamic Random Access Memory).
In order to solve the above problem, a diode architecture in which a TMR element and a diode are serially connected between a bit line and a word line and a simple matrix architecture in which a TMR element is arranged between a bit line and a word line are proposed.
However, since change of magnetization direction of a storage layer is performed by a magnetic field produced by a current pulse in both cases when a data is written in the storage layer, a power consumption is large, and a large capacity cannot be achieved because a wiring layer has an allowable current density limit when the capacity of the memory is increased. The area of a driver for causing a current to flow becomes large only when the absolute value of a flowing current is 1 mA or less or, if the memory is replaced with a DRAM, 2 mA or less. In comparison with another nonvolatile solid-state magnetic memory, e.g., a ferroelectric memory (Ferroelectric Random Access Memory) or a flash memory using a ferroelectric capacitor, a chip size increases to spoil the competitiveness.
With respect to the problem, a solid-state magnetic storage device in which thin film consisting of a high-permeability magnetic material is formed around write wiring layer is proposed. According to this magnetic storage device, since the high-permeability magnetic film is formed around the wiring layer, current value required to write information in magnetic recording layer can be efficiently reduced.
However, even though this device is used, it is very difficult to make a current for writing data 1 mA or less.
In order to solve the above problem, a write method using a spin-injection method is proposed (see the specification disclosed in U.S. Pat. No. 6,256,223, Phys. Rev. B54.9353 (1996), and J. Magn. Magn. Mat.159, L1 (1996)). It is observed that spins are inverted by injection of a spin-polarized current. However, when the spin injection method is applied to a spin tunnel element, a problem that causes element breakdown such as breakdown of the tunnel insulating film arises, and the device has a problem with reliability. A new element structure, a new memory structure, and a new architecture in which, even though data is written by using the spin injection method, a current density in writing performed not to cause element breakdown is decreased and high-speed reading can be achieved must be proposed.
As described above, a new element structure and a new architecture are required to realize a magnetic memory which can operate with low power consumption, which can write data with a low current, which is free from element breakdown, and which has high reliability and a high read speed.